The cabinet or casing for illuminated signs has traditionally been of box-like configuration formed by aluminum extrusions, and is generally arranged so that the assembly is weatherproof for outside use.
The cabinet has either one open face, for mounting a single-faced illuminated sign, or opposed open faces for mounting double-faced illuminated signs.
However, the use of aluminum extrusion for the cabinet has two disadvantages.
First, the aluminum is a rigid material, and if the sign frame is to be hingeable outwardly to open the cabinet for maintenance, some leeway must be provided where the sign frame hooks onto the top of the cabinet. Any such leeway will prevent a snug fit when the sign frame is closed against the cabinet, allowing the sign to rattle, with consequent potential damage, in heavy winds. Also, different widths of extrusion require separate extrusion moulds at a substantial cost per mould. Because of this cost, a relatively small variety of standard widths of aluminum extrusion are available for manufacturing illuminated sign cabinets. In addition, there is a physical limit on the width of aluminum extrusion which can be extruded of 12 to 14 inches. For illuminated sign assemblies with deeper cabinets, widths of extrusion must be fastened together, with consequent loss of weather-proofing.